Textures: Projected Textures
You can either turn Projected Textures on or off. The tooltip reads, "enables the projecting of textures to the environment. Disabling this may greatly improve performance."
Don't disable it, though. As you can see below, I've cast Consecrate in both screen shots. In the first, you can't see the spell at all. In the second, you can. Without textures projected onto the environment, there's a fair chance you'll have trouble with Algalon, Lady Deathwhisper, Halion, and Sindragosa. Any fight where there is something on the ground that you need to avoid becomes significantly harder if you...well, can't see whatever it is you're supposed to be avoiding.
Oh no! Where's the consecrate?
Ah ha, there it is.